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ATEL # 2050; Melania Del Santo (INAF/IASF-Roma), Patrizia Romano (INAF/IASF-Palermo), Lara Sidoli (INAF/IASF-Milano) and Angela Bazzano (INAF/IASF-Roma)
on 18 May 2009; 13:52 UT
Password Certification: Melania Del Santo (firstname.lastname@example.org)
Subjects: X-ray, Binaries, Neutron Stars, Transients
The Very Faint X-ray Transient (VFXT) XMMU J174716.1-281048 (ATel #147 and Sidoli et al., 2006, A&A 456, 287) is being observed with Swift/XRT since May 2007 (ATel #1078), in order to monitor the level of activity during the latest outburst, which started in 2003 (Del Santo et al., 2007, A&A 468, L17; ATels #1078, #1136, #1174, #1496). XMMU J174716.1-281048 is indeed the first source classified as "quasi persistent" VFXT. Previous Swift/XRT observation in April 2008 (ATel #1496) detected the source at a rate of (2.89+/-0.48)E-02 counts/s (0.2-10 keV).
Swift/XRT observed the field of XMMU J174716.1-281048 on 2009 March 5, and, as a pointed target of opportunity observation, on 2009 May 15. The source is still active, with a 0.2-10 keV count rate of (2.51+/-0.66)E-02 and (2.40+/-0.58)E-02 count/s, respectively. The estimated 2-10 keV unabsorbed flux is 2.7E-12 erg/cm2/s (assuming a power law model with a photon index of 2.25, absorbed by a column density of 9E22 cm-2, ATel #1078), which translates in luminosity of 2E34 erg/s (d=8 kpc, as from ATel #1207).
The source luminosity has been constant in this last year, while it has decreased by more than a factor of two with respect to the 2007 Swift (ATel #1078). The duration of the outburst is probably more than six years, confirming the recurrence time estimated by Del Santo et al. (2007, A&A 468, L17).
We will continue the monitoring of the source flux in the next months with Swift/XRT.
We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists as well as the science planners.